If the "Collector" is taking gold from our mines then he's stealing from the kingdom! Bring the Collector to justice, and bring me the ring mentioned in the pickup schedule you gave me. It may tell us whom the Collector is working for...
That Pickup Schedule says the Collector is hiding out at the Brackwell Pumpkin Patch. You should search for him there.
You found him? Well done, <name>. He won't be "collecting" from the Elwynn Mines again!
And this ring you found is interesting... it's a membership ring for the old Stonemason's Guild in Stormwind. Why would a lowly thief have an artisan guild ring, and why are the Defias Thieves collecting money from our mines?
Difficult questions. I hope one day we'll have answers.